Ibn Sīnā—al-Bīrūnī Correspondence—IV

Abstract

In this fourth installment of the correspondence between al-Bīrūnī and Ibn Sīnā, al-Bīrūnī asks eight more questions. His first question is related to the burning of bodies by radiation reflecting off a flask filled with water. The second question pertains to the well-known dispute about the natural tendency of the four elements in their upward and downward movements; the third relates to vision and the fourth deals with the habitation on different quarters of earth. In his fifth question, al-Bīrūnī asks Ibn Sīnā how the two opposite squares in a square divided into four can be tangential. The sixth question is about vacuum. In his seventh question, al-Bīrūnī asks: if things expand upon heating and contract upon cooling, why does a flask filled with water break when water freezes in it? His last question is related to one of the most important observable phenomenon: why does ice float on water?